NMT – A new individual ion counting method: Comparison to a Faraday cup

Determination of epichlorohydrin in water and sewage samples

The GasBench II peripheral along with MAT 253 combination provides a more sensitive platform for the determination of water isotope ratios. Here, we examined the role of adsorbed moisture within the gas chromatography (GC) column of the GasBench II on measurement uncertainties. The uncertainty in 18O/16O ratio measurements is determined by several factors, including the presence of water in the GC. The contamination of GC with water originating from samples as water vapour over a longer timeframe is a critical factor in determining the reproducibility of 18O/16O ratios in water samples. The shift in isotope ratios observed in the experiment under dry and wet conditions correlates strongly with the retention time of analyte CO2, indicating the effect of accumulated moisture. Two possible methods to circumvent or minimise the effect of adsorbed water on isotope ratios are presented here. The proposed methodology includes either the regular baking of the GC column at a higher temperature (120 °C) after analysis of a batch of 32 sample entries or conducting the experiment at a low GC column temperature (22.5 °C). The effects of water contamination on long-term reproducibility of reference water, with and without baking protocol, have been described.

Gas-liqui chromatographic analysis of 2,4-dinitrophenyl-hydrazones of carbonyl compounds

Rapid identification and quantification of toxic alcohols and ethylene glycol is imperative for appropriate treatment. Clinical laboratories frequently rely on direct injection gas chromatography (GC) methods, but these methods require inlet maintenance and multiple GC systems. To overcome these challenges, we developed a single-column headspace GC method for both toxic alcohols and glycols that streamlines patient sample analysis for toxic alcohol ingestion. Optimal parameters for nonderivatized (volatile) and derivatized (glycol) plasma samples were determined using a 7890 A headspace sampler, an Agilent 7697 A GC system, a DB-200 column, and a flame ionization detector. Limit of Quantification (LoQ), linearity, imprecision, carry-over, method comparison, and interference studies were performed using quality control materials and prepared plasma samples. Our volatile method is linear to 3000 mg/L (ethanol) with LoQ concentrations below 20 mg/L (ethanol). The glycol method is linear to 2000 mg/L (ethylene glycol) with LoQ concentrations below 40 mg/L (ethylene glycol). Total assay impression ranged from 1.7% for ethanol to 13.3% for propylene glycol. Both methods were free of sample carryover and compared favorably with a similar clinical method at an outside laboratory. Propionic acid, an accumulating metabolite in methylmalonic acidemia that interferes with ethylene glycol identification by a different method, did not interfere with the ethylene glycol method reported here. Our single-column headspace GC method provides reliable, robust, and rapid identification and quantification of commonly encountered toxic alcohols. Clinical laboratories relying on direct injection Gas Chromatography (GC) for toxic alcohol analysis face challenges including frequent inlet maintenance, sample carryover, or the need for separate GC systems for volatile and glycol analysis. We summarize our development and optimization of two headspace GC methods for nonderivatized (volatile) and derivatized (glycol) plasma samples that use a single DB-200 analytical column. These methods are comparable to other GC methods, not prone to sample carryover, eliminate the need for multiple GC systems or columns, and are readily applicable to other laboratories that provide toxic alcohol analysis.

Methyl tertiary butyl ether (MTBE) is a fuel additive which is used all over the world. In recent years it has often been found in groundwater, mainly in the USA, but also in Europe. Although MTBE seems to be a minor toxic, it affects the taste and odour of water at concentrations of < 30 microg/L. Although MTBE is often a recalcitrant compound, it is known that many ethers can be degraded by abiotic means. The aim of this study was to examine biotic and abiotic transformations of MTBE with respect to the particular conditions of a contaminated site (former refinery) in Leuna, Germany. Groundwater samples from wells of a contaminated site were used for aerobic and anaerobic degradation experiments. The abiotic degradation experiment (hydrolysis) was conducted employing an ion-exchange resin and MTBE solutions in distilled water. MTBE, tertiary butyl formate (TBF) and tertiary butyl alcohol (TBA) were measured by a gas chromatograph with flame ionisation detector (FID). Aldehydes and organic acids were respectively analysed by a gas chromatograph with electron capture detector (ECD) and high-performance ion chromatography (HPIC). Under aerobic conditions, MTBE was degraded in laboratory experiments. Only 4 of a total of 30 anaerobic experiments exhibited degradation, and the process was very slow. In no cases were metabolites detected, but a few degradation products (TBF, TBA and formic acid) were found on the site, possibly due to the lower temperatures in groundwater. The abiotic degradation of MTBE with an ion-exchange resin as a catalyst at pH 3.5 was much faster than hydrolysis in diluted hydrochloric acid (pH 1.0). Although the aerobic degradation of MTBE in the environment seems to be possible, the specific conditions responsible are widely unknown. Successful aerobic degradation only seems to take place if there is a lack of other utilisable compounds. However, MTBE is often accompanied by other fuel compounds on contaminated sites and anaerobic conditions prevail. MTBE is often recalcitrant under anaerobic conditions, at least in the presence of other carbon sources. The abiotic hydrolysis of MTBE seems to be of secondary importance (on site), but it might be possible to enhance it with catalysts. MTBE only seems to be recalcitrant under particular conditions. In some cases, the degradation of MTBE on contaminated sites could be supported by oxygen. Enhanced hydrolysis could also be an alternative.

The method presented describes a sensitive and specific quantitative assay for the simultaneous determination of meperidine and its major metaboUte, normeperidine, in human serum without derivatization. The drugs and internal standard, phencyclidine, are isolated from serum by a basic extraction and back extraction process. The final extract, with methylene chloride as solvent, is quantitated by gas chromatography/mass spectrometry (GC/MS) in the chemical ionization, selected ion monitoring mode of operation. Minimum detectable quantities are 0.17 ng meperidine/mL serum and 0.50 ng normeperidine/mL serum. The coefficient of variation for the quantitative assay is approximately 5%. I n t r o d u c t i o n Since its introduction in 1939 as a synthetic narcotic analgesic (I), meperidine has become one of the primary agents used to alleviate obstetrical pain during the intrapartum period (2). The only known pharmacologically active metabolite of meperidine is normeperidine (3), which is twice as potent a convulsant and one-half as potent an analgesic as the parent drug (4). Both of these agents have been shown to cross the placenta (5). Infants born to mothers who received meperidine during labor have a tendency for lower Apgar scores, increased time to spontaneous respiration (6,7), depressed neonatal oxygen saturation (8), higher arterial partial pressure of carbon dioxide, and lower pH of arterial blood (9). Variability of heart rate (6) and depressed responses to psychophysiologic tests(10) have also been demonstrated in these neonates. In order to characterize the pharmacokinetics of meperidine in the pregnant patient and to correlate physiologic manifestations with blood levels of parent drug and metabolite, a sensitive, reproducible, and rapid method of analysis is needed. The analytical methods curi'ently available do not offer the sensitivity or specificity demanded by this clinical problem. For example, the spectrophotometric method for analysis of these compounds as a methyl orange complex cannot detect less than 0.3 /~g meperidine/mL; in addition, amines other than meperidine and normeperidine react similarly (11). Gas chromatographic (GC) analyses using a flame ionization detector also have insufficient sensitivity, the typical limits of detection being 0.025 ~g/mL for both drugs (12, 13). Derivatization is required in some procedures to use the more sensitive electron capture detector (14) or to oCercome the typically poor chromatographic qualities of normeperidine on most GC columns (15). The major problem affecting these derivatizations is that meperidine and normeperidine often form the same derivatives (14). The specificity of radioimmunoassay procedures currently available is reduced because of cross-reactivity between meperidine and normeperidine (16). The method presented offers simultaneous, sensitive, and specific analysis of meperidine and normeperidine without derivatization. E x p e r i m e n t a l Meperidine and normeperidine were obtained through the courtesy of Wyeth Laboratories (Philadelphia, PA). Phencyclidine was obtained from Applied Science Labs, lnc. (State College, PA). Anhydrous diethyl ether was obtained from Mallinckrodt, Inc. (St. Louis, MO) and methylene chloride, distilled in glass, was obtained from Burdick and Jackson Laboratories, lnc. (Muskegon Ml). All other chemicals were reagent grade. All glassware was acid washed with a mixture of 120 g sodium dichromate, I liter H2SO4 and 1 liter H20. Reacti-vials (Pierce Chemical Company, Rockford, Ik) were silanized with 5% dimethyldichlorosilane (Supelco, Inc., Bellefonte, PA) in toluene. Extraction tubes were silanized by the method of BriStell, et al. (17).

A new marine sediment Standard Reference Material (SRM) has been prepared and analyzed for the determination of trace organic constituents. SRM 1941, Organics in Marine Sediment, has been certified for concentrations of 11 PAHs using results obtained from gas chromatography (GC) with flame ionization detection, gas chromatography-mass spectrometry, and liquid chromatography with fluorescence detection. Non-certified values for 24 additional PAHs are also reported. GC with electron capture detection was used to provide non-certified concentrations for 15 PCB congeners and 7 chlorinated pesticides. In addition to the organic contaminants, concentrations of 32 major and trace elements were determined using neutron activation analysis, and the sulfur content was also determined using isotope dilution thermal ionization mass spectrometry.

Ionization-based detectors for gas chromatography

Ground beef was exposed to aqueous chlorine (600 ppm) for 15 min. to determine whether such exposure might result in the incorporation of organic chlorine into fatty acids or amino acids. Gas liquid chromatography using flame ionization detection (FID) and electron capture detection (ECD) were utilized to evaluate the phospholipid and free fatty acid‐glyceride fractions of the ground beef samples. Analysis by FID suggested that the percentage composition of linoleic, linolenic and arachidonic acids was lower in the phospholipid fraction of the meat samples treated with chlorine. This can be seen by a reduction in peaks for these fatty acids with a concomitant increase in percentage of compounds with a retention time similar to oleic acid. The difference, however, when compared to the control was not significant. The ECD analysis of the free fatty acid‐glyceride fraction indicated formation of chlorinated compounds. The total chlorine content of the treated protein fraction increased as a result of the treatment; but, as reported by others, we are not certain whether the chloride was present as organic chloride or as an inorganic salt. These findings are of importance to the continued use of chlorine as a sanitizer in meat plants because it describes methodology for detecting chloride residues in lipid and protein fractions and indicates that some lipids and possibly some amino acids do react with chlorine.

A method is described for the quantitative determination of saccharin in urine, feces, blood, and animal tissues. The saccharin is extracted with diethyl ether and methylated with methyl iodide to provide a volatile derivative for gas-liquid chromatography. Higher levels, as found in urine and feces, are determined with a flame ionization detector and lower levels, as in blood and tissues, are analyzed with an electron capture detector after a thin layer chromatographic separation.

Evaluation of two commercial capillary columns for the enantioselective gas chromatographic separation of organophosphorus pesticides

The processes of thermal decomposition of analytes in gas chromatographic (GC) columns are classified and two new examples of them are considered in details. First of them is monomolecular decomposition of monoalkyl esters of benzene-1, 2-dicarboxylic (phthalic) acid (monoalkyl phthalates). This process has the analogy in chemical reactions in solutions and it may be responsible for the toxicity of phthalates. The second example is decomposition of non-substituted hydrazones of both aliphatic and aromatic carbonyl compounds. The analytes of the second sub-group present the first example of bimolecular (second order) decomposition in a GC column: two molecules of hydrazones form stable azines and hydrazine. Besides that this process presents the particular interest, because it is accompanied by secondary chemical reactions not in an injector, but within GC column, when a by-product of decomposition is involved into secondary interaction with other constituents of the samples. It was confirmed, that visual images of all these decomposition processes on the chromatograms are rather identical and coincide with the manifestations of interconversion of isomers or tautomers. The most often expressed features of chromatographic profiles in such cases are the presence of peaks of an initial analyte and a product of its decomposition or isomerization, connected with more or less expressed diffused “plateau” or “train” between them. The decomposition processes during sample preparation prior to chromatographic separation or in the heated injector of GC instrument are not accompanied by such features. Despite of the rather “exotic” character of the examples considered, the knowledge of them seems to be useful for better revealing the analogous situations in chromatographic practice. Thermal instability of analytes is the principal restriction of GC separation of reactive compounds and we cannot eliminate it for objective reasons. However, in some cases we can evaluate the temperature limits of chromatographic columns, which should not be exceeded during GC separation of instable compounds. The simplest (low boiling) homologs of thermally unstable compounds are often characterized by “normal” boiling point at atmospheric pressure (Tb, °C) without decomposition, that means the possibility of their GC analysis unambiguously. Therefore, we can select such Tb values as GC and/or GC–MS temperature limit (Tlim) for other members of series of thermally unstable homologs. If GC separation is carried out not in isothermal, but in temperature programming conditions, so-called retention temperature (TR) of unstable analytes should not exceed the evaluated Tlim value.

Construction and validation of an automated spray-and-trap gas chromatograph for the determination of volatile organic compounds in aqueous samples

High aspect ratio nickel microfluidic columns were fabricated using the LiGA technique. The 2-m-long 50-mum-wide high aspect ratio columns will be the separation component of a handheld gas chromatograph device for detecting semivolatile and volatile compounds. As a first step, 600-mum-deep electrodeposited nickel columns were fabricated. The serpentine columns were sealed and pressure-flow rate characteristics compared with the theoretical values. The response of the sealed columns was studied by running methane gas plugs through uncoated columns with a flame ionization detector at the exit. Negligible flow-induced dispersion was observed in the sealed metal columns. Unretained peak widths of ~15 ms were measured, and the experimental pressure and flow rate distributions matched those predicted by established analytical models within plusmn2.5%. Columns were coated with OV-1 stationary phase using static coating methods. A mixture of four hydrocarbons C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> , C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> , and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> was separated in a coated 50 mum by 600 mum by 0.5 m column in less than 2 s at 70 degC

Gas chromatography with flame ionization and flameless sulfur chemiluminescence detectors in series for dual channel detection of sulfur compounds